In the field of generators using an indirect cooling system that cools by sending hydrogen gas or air to the outside of a coil provided with an insulation layer, the achivement of a high thermal conductivity in a thickness direction of the insulation layer of the coil is desired.
Prepreg mica tapes composed of a resin, mica, and a backing material are often used as the insulation layer of a coil. In order to improve the thermal conductivity of the prepreg mica tapes, in many cases, a technique of adding an inorganic filler having a higher thermal conductivity than a resin and mica into the tapes is employed.
There are cases in which the prepreg mica tapes are required to have flexibility in terms of facilitating coil taping work.
For example, Table 1 and Examples 3 and 4 of Japanese Patent Application Laid-Open (JP-A) No. 2005-199562 disclose mica tapes each in which, as an inorganic filler, an alumina having a high thermal conductivity is filled in mica, and show that mica tapes having thermal conductivities of from 0.32 W/m·K to 0.36 W/m·K can be obtained.
In addition, Table 1 and Examples 1 to 7 of JP-A No. 2000-116047 disclose mica tapes each in which an alumina having a high thermal conductivity as an inorganic filler is filled in a resin, and show that mica tapes having thermal conductivities of from 0.40 W/m·K to 0.60 W/m·K can be obtained.